Trifolium ambiguum (Caucasian clover) is being released in New Zealand for use in areas where growth of T. repens (white clover) is marginal. Although closely related to T. repens, T. ambiguum has unique and highly specific nodulation requirements and as rhizobial strains capable of effectively nodulating T. ambiguum are not naturally found in New Zealand soils, they must be introduced with the seed. Rhizobium leguminosarum bv. trifolii strains such as ICC105 form effective nodules on T. ambiguum but ineffective (Fix⁻) nodules on T. repens. The T. repens nodules nevertheless develop normally and contain bacteroids. R. l. bv. trifolii strains that are effective on T. repens such as NZP561, fail to nodulate T. ambiguum. As the host-specific nitrogen fixation defect of Caucasian clover rhizobia on T. repens has potentially adverse agronomic implications, the genetic basis for this Fix⁻ phenotype was investigated. Rhizobium leguminosarum bv. trifolii strain ICC105 was converted to Fix⁺ on T. repens by the introduction of an 18-kb fragment of DNA from a white clover rhizobial strain (NZP514) symbiotic plasmid. This fragment contained several nif and fix genes, including nifHDKEN, fixABCX, nifA, nifB, fdxN and fixU. Tn5 mutation of these white clover rhizobial genes demonstrated that most were required to impart the Fix⁺ phenotype on T. repens to ICC105, with the exception of nifA. Mutagenesis of the ICC105 nifA gene and subsequent complementation with various combinations of the white clover rhizobia nif/fix genes as well as transcriptional lacZ fusion studies of the ICC105 nifA and nifH genes demonstrated that ICC105 nifA is expressed and functional during the ineffective nodulation of T. repens and able to activate expression of nifHDKEN and fixABCX operons derived from white clover rhizobium but not from ICC105. Sequence analysis and comparison of the intergenic region between the divergently transcribed nif/fix operons revealed a conserved 111-bp region found between the nifH/fixA promoters of Caucasian clover rhizobia, but not in white clover rhizobia. Attempts to modify this region in ICC105 failed in creating a strain which was Fix⁺ on T. repens; however recombination of the nifHD/fixAB region from a white clover rhizobium into the ICC105 genome produced several strains with a �swapped� nitrogen fixation phenotype (i.e. Fix⁺ on T. repens and Fix⁻ on T. ambiguum). A hypothesis was therefore proposed by which differences in the nifH/fixA promoter regions of Caucasian clover rhizobia and white clover rhizobia modulate the expression of the upstream genes in response to the particular plant host they are nodulating. The incompatibility between the symbiotic plasmid of R. l. bv. trifolii ICC105 and the white clover rhizobium symbiotic plasmid cointegrate, pPN1, was also investigated and potential regions of each plasmid involved in this incompatibility were identified. The research presented in this thesis has contributed to the genetic knowledge of the nitrogen fixation genes, and regulation of these genes in R. l. bv. trifolii. It has also provided progress towards the goal of creating a suitable inoculant strain for T. ambiguum that is able to fix nitrogen in symbiosis with both T. repens and T. ambiguum.

Bibliography: leaves 213-229. / xxiii, 229, 26 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 2000

Bibliography: leaves 146-170. / xix, 170 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Soil and Water, Waite Agricultural Research Institute, University of Adelaide, 1994

Although legumes have been widely studied for their nitrogen-fixing ability, it is uncertain to what extent legume cover crops achieve their nitrogen-fixing potential under the climatic conditions encountered in western Oregon. Furthermore, it is unknown what factors control the proportions of legume cover crop N that are either sequestered into soil organic matter, or that contribute to the N requirements of the following summer crop. Soil was sampled in mid-September 1997, after harvest of a summer broccoli crop, from plots located at the North Willamette Research and Extension Center, Aurora, Oregon. Soil was sampled from main plots that had been either winter cover cropped with red clover (LN��� and LN���) or fallowed during the winter period (FN��� and FN���), and specifically from sub-plots in which the following summer crop had received either zero (N���) or an intermediate (N���) rate of N fertilizer as urea. Levels of total organic carbon (TOC), total Kjeldahl nitrogen (TKN), and readily mineralizable C and N were measured in both whole soil samples and in different aggregate-size classes (<0.25, 0.25-0.5 0.5-1.0, 1.0-2.0, and 2-5mm) prepared by dry sieving the soil. Aggregate size-class distribution was not affected by the cover crop treatment. Although there was no significant effect of cover crop treatment on either TKN or TOC levels in whole soil samples, TOC levels were consistently higher in the small aggregate size-classes <1 mm of the fallow than the legume treatment. There was a significantly higher level of mineralizable C in the <0.25 mm size class of the legume than the fallow treatment. There was a trend for the level of mineralizable N to be greater in soil from the legume than the fallow treatment. However, N fertilizer had a significant positive effect on the level of readily mineralizable N in both fallow and legume cover-cropped treatments, it had a negative effect on TKN levels among all aggregate-size classes. There were differences in the levels of mineralizable N measured among the aggregate-size classes, and immobilization of N between 20 and 40 days of incubation also differed among the aggregate-size classes. / Graduation date: 1999

Kura clover (Trifolium ambiguum) is a perennial legume species that has been found to have exceptional persistence in the United States, Australia and New Zealand. There are two challenges that impede the incorporation of Kura clover into pasture mixtures in Alberta. The first is the lack of available seed, and the second is poor establishment success in mixtures with highly competitive grass species. A series of experiments were conducted to (i) address the potential for seed production in a central Alberta environment and (ii) to determine alternative strategies for establishment in mixtures. Kura clover successfully flowered and produced seed under central Alberta growing conditions. Seed production was greater from the cultivar Endura than Cossack. Kura clover seed production was not affected by row spacing however, yield was greater when clover was planted at 3 or 6 kg/ha versus 9 or 12 kg/ha. Seed yield ranged from 80 kg/ha to 350 kg/ha. Establishing Kura clover with a cover crop reduced flowering and seed production. Corn (Zea mays) was the least competitive cover crop, followed by faba bean (Vicia faba L.). Canola (Brassica napus), peas (Pisum sativum L.), barley (Hordeum vulgare) and triticale (X Tritosecale) reduced Kura clover seed yield and are not recommended as cover crops. Comparison of above and below ground competition between Kura clover and meadow bromegrass (Bromus biebersteinii), indicated that below ground competition has the greatest impact on Kura clover seedling growth. Altering seeding rate and delaying introduction of the grass species by up to two months significantly improved Kura clover establishment in mixtures. Kura clover survival in established pastures was higher with physical than chemical sod suppression of the standing forage. Dry matter yield of Kura clover was greatest when defoliated at 6 week intervals. Challenges still remain regarding seed production and establishment of Kura clover. However, we successfully addressed the major concerns regarding the potential of Kura clover in Alberta. / Plant Science

A field experiment from 2003 to 2005 at two sites examined the impacts of forage species and legume proportion on forage sward production. Grasses generally established rapidly and out-yielded swards high in legume content, although legumes did improve forage quality. Alfalfa was retained at greater relative biomass in mixed swards than swards containing clover. Legume persistence also varied depending on neighbouring grass species. A greenhouse study examined competitive interactions between Canada thistle (a common pasture weed), white clover and Kentucky bluegrass during establishment. Although thistle was most susceptible to intra-specific competition, and strongly affected forage yield, the latter also influenced weed biomass. Competitiveness of forages depended directly on soil medium, emphasizing the importance of abiotic factors on vegetation dynamics in mixed swards. / Rangeland and Wildlife Resources

Excessive growth by red clover, Trifolium pratense L., grown for seed interferes with maximum seed production and harvest in Oregon's Willamette Valley. This study was conducted during 1986 and 1987 on red clover cv. Kenland to determine if plant height and dry matter production could be inhibited and seed yields improved with the plant growth regulators (PGRs) uniconazol (XE-1019) and paclobutrazol (Parlay). The effects of different soil-applied and foliar-applied PGRs and application rates on plant height, crop biomass, and yield components of red clover were measured at Corvallis, OR on Woodburn silt-loam (fine-silty mixed mesic Aquultic Argixerolls) soil. Soil-applied PGRs were also managed under single and multiple irrigation regimes in 1986. Under a single irrigation regime in 1986, canopy height was reduced by 32% when XE-1019 was applied at 1.12 kg ai/ha and was reduced by 13% when Parlay was applied at 1.68 kg ai/ha. Averaged over the two-year period, straw yield was reduced 40% with XE-1019 (1.12 kg ai/ha) and by 12% with Parlay (1.68 kg ai/ha). Seed yield was increased by 11% with the lower XE-1019 rate (0.14 kg ai/ha) and was increased by 14% with the higher Parlay rate (1.68 kg ai/ha). Soil-applied PGR treatments reduced canopy height by 25% with XE-1019 (1.12 kg ai/ha) and was reduced by 11% with Parlay (1.68 kg ai/ha) under multiple irrigation in 1986. Straw yield was reduced by 30% with XE-1019 (0.84 kg ai/ha), but Parlay had no effect on straw yield. In addition, seed yield was increased by 8% with XE-1019 (0.56 kg ai/ha) and by 18% with Parlay (1.68 kg ai/ha). Foliar-applied XE-1019 (1.12 kg ai/ha) reduced canopy height by 13% in 1986 and by 25% in 1987, whereas foliar-applied Parlay (1.12 kg ai/ha) reduced canopy height by 9% in 1986 and by 19% in 1987. In 1986, seed yield increases averaged 16% across all 3CE-1019 treatments (0.07 to 1.12 kg ai/ha) and was increased an average of 21% across all Parlay treatments (0.28 to 1.68 kg ai/ha). However, 1987 was drier and warmer than 1986, consequently, foliar-applied XE-1019 reduced seed yields by an average of 23% and Parlay reduced seed yields by an average of 21%. Total dry weight and straw weight were unaffected by foliar-applied PGR treatment in both years. Use of XE-1019 and Parlay in field crop production has the potential to reduce dry matter production and improve seed recovery, but results vary from year to year. These PGRs have the potential to improve seed yields and may be effective in improving harvest conditions by reducing vegetative biomass. / Graduation date: 1995

Tiriamojo darbo objektas - tirtos daugiamečių žolių veislės: raudonieji dobilai ‘Liepsna’, baltieji dobilai ‘Bitūnai’ ir rausvieji dobilai “Daubiai“, pasėti mišinyje su varpinėmis žolėmis: pašariniais motiejukais, tikraisiais eraičinais, daugiametėmis svidrėmis , pievinėmis miglėmis. Tyrimo tikslas – 1. nustatyti Rizobakterijų gumbelių skaičiuų ir masę skirtingose ankštinėse žolėse; 2. nustatyti biologinio azoto sukaupimą žolynų agrocenozėse. Tyrimo metodika. Tyrimai buvo vykdyti 2008 m. Lietuvos žemės ūkio universiteto bandymų stotyje ir Vėžaičiuose įvairiuose laukuose, kurių tikslios charakteristikos nepavyko sužinoti. Iš kiekvieno lauko paimti ir iškasti 10 augalų su šaknimis: 10 raudonųjų dobilų (Trifolium pratense L), 10 baltųjų dobilų (Trifolium repens L.) ir 10 rausvųjų dobilų (Trifolium hybridum L). Paimti augalai atsargiai nuplauti ir suskaičiuoti ant kiekvieno augalo šaknų esantys gumbeliai. Suskaičiuoti gumbeliai pasverti. Gumbelių analizė atlikta dobilų žydėjimo metu. Laikėme, kad m-2 buvo 10 augalų. Rhizobakterijų gumbelių skaičius hektare paskaičiuotas vnt.m-2 padauginus iš 10000. Tyrimo rezultatai. 1. Vidutiniais duomenimis daugiausiai (102 vnt.) gumbelių priskaičiuota ant raudonųjų dobilų šaknų, mažiau (97 vnt.) ant baltųjų dobilų ir mažiausiai (72 vnt.) ant rausvųjų dobilų šaknų. Rhizobakterijų gumbelių masė ant skirtingų dobilų rūšių šaknų įvairavo 0,03-0,05 g ribose. 2. Tarp visų dobilų rūšių gumbelių skaičiaus ir jų masės nustatytas stiprus koreliacinis... [toliau žr. visą tekstą] / The aim of investigation was to determine number and weight of nodules formed on the roots of varios perennial leguminous grasses. 1. The highest midle number 102 of Rhizobacterial nodules was determined on red clover roots. On the roots of whete 97 clover were less Rhizobacterial nodules and the least Rhizobacterial nodules number 72 defined on alsike clover roots. 2. The weight of Rhizobacterial nodules on different clover species roots difered between 0,03 – 0,05 g.

Legumes fix atmospheric nitrogen (N) via symbiotic biological N fixation where part of the N fixed by legumes can be transferred to non-legumes. Identification of genotypic variability for N transfer among different legume cultivars enables improving N transfer to non-legumes under mixed stands. Six diverse red clover (RC) cultivars which include three diploid (AC Christie, Tapani and CRS15) and three tetraploid (Tempus, CRS18, CRS39) were selected to evaluate genotypic variability for N transfer. The above RC cultivars were characterized for root hair deformation, nodulation, growth, and N uptake under different levels of N supply during the growing period and for starter N supply under in vitro conditions. Significant genotypic differences among the RC cultivars were found for the above attributes where the cultivars responded differently to N applications during early growth. The above RC cultivars were also evaluated for root exudate N content in the form of NO3--N, NH4+-N and dissolved organic N (DON) during early growth under in vitro conditions. Significant genotypic differences were found for root exudate inorganic and organic N content. In general, root exudate DON content was greater than the inorganic N content and positively correlated with average nodule dry weight and shoot N concentration. The NH4+-N and NO3--N content in root exudates were positively correlated with active nodule number and root growth parameters respectively. Nitrogen fixation, N transfer ability and soil N profiles of the above six RC cultivars were evaluated with bluegrass under field conditions for two post establishment years. Significant genotypic differences were found for N fixation and transfer but, these attributes were not associated with the ploidy nature of the selected RC cultivars. Generally, N transfer increased as the season and production year advanced. Soil mineral N and potential N leaching were affected differently by the RC cultivars included in this study under mixed stands, thus showing genotypic differences for soil N cycling. The results of investigations in this thesis highlight the dynamics of N flow between legumes and companion grasses and may assist in developing management protocols and plant breeding strategies to identify genotypes with efficient N cycling profiles.

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